In general, sanitary pressure sensors used in, for example, facilities for manufacturing food, medical supplies, etc., which require sanitary care, are expected to satisfy strict requirements regarding, for example, corrosion resistance, cleanliness, reliability, and versatility.
For example, to satisfy the requirements regarding corrosion resistance, a liquid contact portion of a sanitary pressure sensor that comes into contact with fluid (for example, liquid) to be subjected to pressure measurement needs to be made of a highly corrosion-resistant material, such as a stainless steel (SUS), a ceramic, or titanium. In addition, to satisfy the requirements regarding cleanliness, the sanitary pressure sensor needs to have a flush diaphragm structure that enables easy cleaning and to be highly thermal-shock resistant to withstand steam washing. In addition, to satisfy the requirements regarding reliability, the sanitary pressure sensor needs to have an encapsulant-free structure (oil-free structure) and a structure in which a diaphragm does not easily break (high rigidity barrier). In addition, to satisfy the requirements regarding versatility, a connecting portion of the sanitary pressure sensor to be connected to a pipe through which the fluid that serves as a measurement object flows needs to have the shape of a coupling.
As described above, the material and structure of the sanitary pressure sensor are more strictly limited than those of other pressure sensors, and therefore the sensitivity of the sanitary pressure sensor cannot be easily increased. For example, when the film thickness of the diaphragm is increased (aspect ratio of diameter to thickness of the diaphragm is reduced) to realize a structure in which the diaphragm does not easily break, the amount of deformation of the diaphragm is reduced, and the sensitivity of the sensor is reduced accordingly. Therefore, a technology for accurately detecting a small amount of deformation of the diaphragm in the sanitary pressure sensor is desired.
For example, PTL 1 and PTL 2 disclose load converting pressure sensors including a semiconductor chip (beam member) made of, for example, Si on which a strain gauge including diffused resistors is formed. To increase the sensitivity of the sensor, only a displacement of a central portion of a diaphragm is transmitted to the semiconductor chip, and changes in the resistances of the diffused resistors due to the piezoresistive effect based on deformation of the semiconductor chip are detected.
More specifically, in the load converting pressure sensors according to the related art disclosed in PTL 1 and PTL 2, a central portion of the semiconductor chip is supported at a central portion of the diaphragm, and both ends of the semiconductor chip are fixed to portions that do not substantially move. For example, according to PTL 1, a strip-shaped semiconductor chip is supported at the center thereof by a rod-shaped member called a pivot at the center of a diaphragm. Both ends of the semiconductor chip in a long-side direction are fixed to a thick portion formed at the outer rim of the diaphragm with insulating pedestals interposed therebetween. According to PTL 2, the center of a rectangular semiconductor chip is fixed to the center of a diaphragm, and both ends of the semiconductor chip in the long-side direction are fixed to a base that does not move.